Respirators operating independently from the ambient atmosphere, so-called freely portable isolating devices, are generally known. They offer protection, among other things, against lack of oxygen and against toxic substances, especially toxic gases, from the ambient atmosphere. Defined breathing gases are fed to the user by means of the respirator. The breathing gases may consist of air or oxygen, possibly as a mixture with other suitable gases such as nitrogen.
In case of freely portable isolating devices, distinction can be made between container type devices, e.g., with compressed air (compressed air devices, also called compressed air breathing apparatuses), and regeneration type devices. In container type devices with compressed air, the latter is carried along as a reserve, for example, in pressurized cylinders, and carbon dioxide-containing expired air is removed into the ambient atmosphere. Thus, the duration of use per mission is limited in case of container type devices; in addition, it depends, among other things, on the user's build and the particular use and is usually in a range of 20 minutes to 60 minutes. In case of a regeneration type device, the user is supplied with oxygen from an oxygen reserve carried along in the device. For example, compressed oxygen, compressed oxygen-nitrogen mixtures or chemically bound oxygen are considered for use as an oxygen reserve. However, contrary to the container type device, the expired gas is not released into ambient atmosphere through an expiration valve, but is at least partly regenerated in the device. The carbon dioxide (CO2) contained in the expired gas is removed at least partly. The expired gas is usually sent for this via or through a regenerating material, which is normally present in a regenerating cartridge, through which the breathing gas flows, is bound by same, and is thus removed from the expired gas. The oxygen consumed by the user is complemented from the reserve as needed and the regenerated breathing gas, which is optionally enriched with oxygen, is again fed to the user. This “circuit” leads to a considerably prolonged duration of use per mission. Such respirators are also called closed-circuit respirators.
A slight vacuum is generated in the mask space of the breathing mask of the respirator during inspiration by the user in prior-art freely portable isolating devices with normal pressure. If a leak develops in the device in the vacuum range, i.e., a lack of tightness of the breathing mask due to the breathing mask slipping on the user's face, toxic substances, such as toxic particles or undesired gases, could penetrate from the ambient atmosphere into the breathing gas circulation in the device, and these are then possibly inhaled by the user.
To prevent or reduce the penetration of toxic substances, devices with overpressure are preferred, in which a slight overpressure of the breathing gas constantly prevails in the mask space. Since there is consequently a pressure gradient from the mask space to the ambient atmosphere all the time, only breathing gas can flow off to the outside in case of a possible leak, but no gas can enter the breathing gas circulation from the ambient atmosphere. However, it is disadvantageous here that the breathing gas reserve is consumed rapidly due to the uncontrolled discharge and the duration of use of the respirator is thus undesirably shortened. It is of great significance that the user be informed of the leak especially if an unnoticed slip of the mask occurs, e.g., because of major stresses on the part of the user or when working in tight surroundings.
There is a permanent pressure measurement and display (pressure gauge) in generally known devices, as a result of which the user is continuously informed of the breathing gas reserve available to him. A warning means indicates when the breathing gas reserve comes to an end. However, this type of measurement of the state provides no information on whether a high oxygen consumption has developed because of increased respiratory activity or a leak.
DE 3930362 C2 describes the switching off of the overpressure in a closed-circuit respirator with overpressure operation in case of an excessively high oxygen consumption. The oxygen consumption is determined in the device being described by measuring the flow of oxygen from a compressed gas cylinder carried along by means of a flow measuring means directly behind the pressure reducer connected to the compressed gas cylinder. To determine whether the excessively high oxygen consumption from the compressed gas cylinder carried along has developed because of a leak or because of a higher oxygen consumption by the user, the oxygen consumption is determined on the basis of the flow of oxygen during the expiration phase of the user only. The consumption is compared with a preset limit value and the overpressure is switched off in case the limit value is exceeded. However, this process functions only in devices with demand-controlled respiration by means of demand oxygen systems, e.g., in compressed air breathing apparatuses. By switching off the overpressure, the outflow of the breathing gas from the device because of the leakage is reduced and the service life of the closed-circuit respirator is thus prolonged. However, undesired gases may enter the breathing circulation from the ambient atmosphere, e.g., toxic gases, such as CO, because of the lack of overpressure in the closed breathing circuit.
Other prior-art regeneration type devices, e.g., model PSS BG4 (Dräger), usually operate, based on their principle of action, usually with a volume-controlled breathing gas demand. Oxygen is now introduced continuously into the closed breathing circuit via a constant dispensing. If the breathing gas consumption is increased as a consequence of a higher stress of the user or because of a leak, oxygen is additionally dispensed into the breathing gas circulation via a minimum valve. The minimum valve is opened when the gas volume in the breathing gas circulation has dropped below a certain value, e.g., when a breathing bag used for volume compensation is empty. The volume removed from the oxygen cylinder cannot be higher at any time than the volume of oxygen that has been uniformly introduced into the breathing circuit by the constant dispensing during the expiration phase of the user, even in case of an existing leak in the system. This results from the fact that an increased oxygen consumption is possible only by opening the minimum valve, which dispenses a volume flow of more than 80 L/minute into the breathing bag. However, this is opened only when the breathing bag is empty. However, the breathing bag is filled with the expired gas volume during the expiration phase of the user, assuming that the components in the expiration branch of the device do not have a major leak, e.g., an expiration tube that is not connected.